Method and apparatus for synchronizing an adaptable security level in an electronic communication

ABSTRACT

A method of communicating in a secure communication system, comprises the steps of assembling as message at a sender, then determining a security level, and including an indication of the security level in a header of the message. The message is then sent to a recipient.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for providing synchronizing an adaptable security level in an electronic communication.

2. Description of the Prior Art

In electronic communications, it is often necessary to prevent an eavesdropper from intercepting a message. It is also desirable to have an indication of the authenticity of a message, that is a verifiable identification of the sender. These goals are usually achieved through the use of cryptography. Private key cryptography requires sharing a secret key prior to initating communications. Public key cryptography is generally preferred as it does not require such a shared secret key. Instead, each correspondent has a key pair including a private key and a public key. The public key may be provided by any convenient means, and does not need to be kept secret.

There are many variations in cryptographic algorithms, and various parameters that determine the precise implementation. In standards for wireless communications, it has been customary to set these parameters in advance for each frame type. However, this approach limits the flexibility of the parameters.

When one device is communicating with several other devices, it will often need to establish separate parameters for each communication.

It is an object of the present invention to obviate or mitigate the above disadvantages.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there is provided a method of communicating in a secure communication system, comprising the steps of assembling as message at a sender, then determining a security level, and including an indication of the security level in a header of the message. The message is then sent to a recipient.

In accordance with another aspect of the present invention, there is provided a method of providing a security level to a sender by including information in an acknowledgement message.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the preferred embodiments of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein:

FIG. 1 is a schematic representation of a communication system;

FIG. 2 is a schematic representation of an information frame exchanged in the communication system of FIG. 1;

FIG. 3 is a schematic representation of a frame control portion of the frame of FIG. 2;

FIG. 4 is a schematic representation of a method performed by a sender in FIG. 1;

FIG. 5 is a schematic representation of a method performed by a recipient in FIG. 1;

FIG. 6 is a schematic representation of a network protocol used in one embodiment of the communication system;

FIG. 7 is a schematic representation of an embodiment of the communication system;

FIG. 8 is a schematic representation of another embodiment of the communication system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a communication system 10 includes a pair of correspondents 12, 14 connected by a communication link 16. Each correspondent 12, 14 includes a respective cryptographic unit 18, 20.

Each correspondent 12, 14 can include a processor 22, 24. Each processor may be coupled to a display and to user input devices, such as a keyboard, mouse, or other suitable devices. If the display is touch sensitive, then the display itself can be employed as the user input device. A computer readable storage medium is coupled to each processor 22, 24 for providing instructions to the processor 22, 24 to instruct and/or configure processor 22, 24 to perform steps or algorithms related to the operation of each correspondent 12, 14, as further explained below. The computer readable medium can include hardware and/or software such as, by way of example only, magnetic disks, magnetic tape, optically readable medium such as CD ROM's, and semi-conductor memory such as PCMCIA cards. In each case, the medium may take the form of a portable item such as a small disk, floppy diskette, cassette, or it may take the form of a relatively large or immobile item such as hard disk drive, solid state memory card, or RAM provided in a support system. It should be noted that the above listed example mediums can be used either alone or in combination.

Referring to FIG. 2, a frame used in communications between the correspondents 12, 14 is shown generally by the numeral 30. The frame 30 includes a header 32 and data 34. The header 32 includes information about the source and destination of the frame 30 and is used for processing frames. The header 32 may contain other control information as will be understood by those skilled in the art.

Referring to FIG. 3, the header 32 also contains frame control bits 33. The frame control bits 33 include security bits 35, 36, and 37. Security bit 35 indicates whether encryption is on or off. Security bits 36 and 37 together indicate the integrity level, such as 0, 32, 64, or 128 bits. It will be recognized that providing security bits in each frame allows the security level to be modified on a frame-by-frame basis rather than on the basis of a pair of correspondents, therefore providing greater flexibility in organizing communications.

In order to provide security, certain minimum security levels may be used. These levels should be decided upon among all of the correspondents through an agreed-upon rule. This rule may be either static or dynamic.

In operation, the correspondent 12 performs the steps shown in FIG. 4 by the numeral 100 to send information to the correspondent 14. First, the correspondent 12 prepares data and a header at step 102. Then it selects the security level at step 104. The security level is determined by considering the minimum security level required by the recipient, the nature of the recipient, and the kind of data being transmitted. If the security level includes encryption, then the correspondent 12 encrypts the data at step 106. If the security level includes authentication, then the correspondent 12 signs the data at step 108. Then the correspondent 12 includes bits indicating the security level in the frame control at step 110. The correspondent 12 then sends the frame to the correspondent 14.

Upon receiving the frame, the correspondent 14 performs the steps shown in FIG. 5 by the numeral 120. The correspondent 14 first receives the frame at step 122. It then extracts the security bits at step 124. If the security bits indicate encryption, then the correspondent 14 decrypts the data at step 126. If the security bits indicate authentication, then the correspondent 14 verifies the signature at step 126. Finally, the correspondent 14 checks the security level to ensure it meets predetermined minimum requirements. If either the encryption or authentication fails, or if the security level does not meet the minimum requirements, then the correspondent 14 rejects the message.

It will be recognized that providing security bits and an adjustable security level provides flexibility in protecting each frame of the communication. It is therefore possible for the sender to decided which frames should be encrypted but not authenticated. Since authentication typically increases the length of a message, this provides a savings in constrained environments when bandwidth is at a premium.

In a further embodiment, the correspondent 12 wishes to send the same message to multiple recipients 14 with varying minimum security requirements. In this case, the correspondent 12 chooses a security level high enough to meet all of the requirements. The correspondent 12 then proceeds as in FIG. 4 to assemble and send a message with the security level. The message will be accepted by each recipient since it meets each of their minimum requirements. It will be recognized that this embodiment provides greater efficiency than separately dealing with each recipient's requirements.

In another embodiment, a different number of security bits are used. The actual number of bits is not limited to any one value, but rather may be predetermined for any given application. The security bits should indicate the algorithm parameters. They may be used to determine the length of a key as 40 bits or 128 bits, the version of a key to be used, or any other parameters of the encryption system.

It will be recognized that in the above embodiments, a network stack may be used to organize communications between the correspondents. Referring therefore to FIG. 6, the a network stack of correspondent A is shown by the numeral 130. A network stack of correspondent B is shown by the numeral 140. The network stacks are organized into layers and have similar structures. The network stack 130 includes an application layer (APL) 132, a network layer (NWK) 134, a message authentication layer (MAC) 136, and a physical layer (PHY) 138. The network stack 140 includes similar components with similar numbering.

The sender determines how he wants to protect payload (and where to protect it, i.e., which layer). For the APL layer, security should be transparent; its role is limited to indicating at which level it wants to protect data (i.e., security services: none, confidentiality, data authenticity, or both). The actual cryptographic processing then is delegated to lower layers.

The recipient determines whether or not to accept protected payload, based on the received frame and locally maintained status information. The outcome of the cryptographic processing (done at the same layer as that of the sender), including info on the apparently offered protection level, is passed to the application layer, who determines whether the offered protection level was adequate. The recipient may acknowledge proper receipt of the frame to the original sender, based on this ‘adequacy test’.

The acknowledgement (ACK), if present, is then passed back to the sender and passed up to the appropriate level (if protected message sent at APL layer, then ACK should also arrive back at that level; similar for lower layers of course).

The sender A determines that it wants to protect payload m using the protection level indicated by SEC (taking into account its own security needs and, possibly, those of its intended recipient(s). The payload m and desired protection level SEC is then passed to a lower layer (e.g., the MAC layer, as in the diagram) which takes care of the actual cryptographic processing. (This message passing could include additional status information that aids in the processing of the frame, such as the intended recipient(s), fragmentation info, etc. Note that the delegation of the cryptographic processing to a lower layer is only a conceptual step if cryptographic processing takes place at the same layer at which the payload m originates.) Cryptographic processing involves protecting the payload m and, possibly, associated information such as frame headers, using the cryptographic process indicated by the desired protection level SEC. The key used to protect this information is derived from shared keying material maintained between the sender and the intended recipient(s). After cryptographic processing, the protected frame, indicated by [m]K, SEC in FIG. 6, is communicated to the intended recipient(s) B.

The intended recipient (s) retrieves the payload m′ from the received protected frame, using the cryptographic process indicated by the observed protection level SEC′, using a key that is derived from shared keying material maintained between the sender and the recipient(s) in question. The retrieved payload m′ and the observed protection level SEC′ is passed to the same level at which the payload was originated by the sender, where the adequacy of the observed protection level is determined. The observed protection level SEC′ is deemed sufficient, if it meets or exceeds the expected protection level SEC₀, where the parameter SEC₀ might be a fixed pre-negotiated protection level that does or does not depend on the retrieved payload m′ in question. (Defining SEC₀ in a message-dependent way would allow fine-grained access control policies, but generally involves increased storage and processing requirements.)

The above approach works in contexts where expected and observed protection levels can be compared, i.e., where the set of protection levels is a partial ordering. An example is the context where protection involves a combination of encryption and/or authentication, with as ordering the Cartesian product of the natural ordering for encryption (encryption OFF<Encryption ON) and the natural ordering of authentication (ordered according to increasing length of data authenticity field). Moreover, if the set of protection levels has a maximum element, then the sender can use this maximum protection level to ensure that (unaltered) messages always pass the adequacy test.

In the above embodiments, each sender has to pre-negotiate the minimum expected protection level SEC₀ with each intended recipient. Thus, the approach might not be as adaptive as desirable for some applications and may involve additional protocol overhead at every change of the SEC₀ parameter. These disadvantages can be overcome by using the acknowledgement (ACK) mechanism from recipient(s) to sender as a feedback channel for passing the SEC₀ info. This is performed by incorporating in each acknowledgement message an indication as to the expected protection level. This information can then be collated by the original sender to update the minimum protection level expected by its recipient(s), whether or not this is message-dependent or not.

In a further embodiment, a method of synchronizing security levels is shown. Referring to FIG. 7, another embodiment of the communication system is shown generally by the numeral 160. The system includes a sender A 162 and recipients 168 in a group labelled G. The sender A includes parameters SEC_(A) 164 and SEC_(G) 166.

Sender A wants to securely communicate a message m to a group G of devices. The sender A has access to the two parameters, i.e.,

-   -   (1) The minimum level SEC_(A) at which it would like to protect         this message (in general, SEC_(A) might depend on the group it         sends information to and the message itself, so proper notation         would be SEC_(A) (m,G));     -   (2) The minimum protection level SEC_(G) that the group G of         recipients expects (again, the proper notation would be         SEC_(G)(m,A) if this level would depend on the sender and the         message itself as well). Here, the minimum expectation level of         a group is the maximum over all group members of the minimum         expectation level for each group member.

Initialization

Sender A assumes that each parameter SEC_(G) is set to the maximum protection level (for each group G it securely communicates with).

Operational Usage

-   -   Sender A determines the minimum protection level SEC_(A) at         which it wants to protect the message m. The actual protection         level SEC applied to the message m meets both its own adequacy         test (i.e., SEC≧SEC_(A)) and the minimum expected level by the         group G (i.e., SEC≧SECG).     -   Each recipient B that is in the group G of recipients (i.e., B         ε G) indicates in its secure acknowledgement message the minimum         expected protection level (for sender A and message m) at that         particular moment of time.     -   A updates the parameter SEC_(G) such that it is consistent with         all the minimum protection levels indicated in each of the         acknowledgement messages it received back (i.e., SECG≧SECB for         all responding devices B).

Note that the procedure described above sends messages with a protection level that satisfies both the needs of the sender and expectations of recipient(s) and is adaptable to changes herein over time. Alternatively, the sender might only take its own protection needs into account, at the cost of potentially sending messages that will be rejected by one or more recipients due to insufficient—since less than expected—protection level.

The procedure described above can be generalized towards a general self-synchronization procedure for status information among devices in any network topology, where the feedback info on status information may be partially processed along the feedback path from recipient(s) towards sender already, rather than at the sender itself only (in the example above, this graph is a tree with root A and leaves the recipient(s) and the synchronization involves a specific security parameter).

As seen in FIG. 8, A sends a payload secured at protection level SEC to a group of devices consisting of B1-B4. The recipients B1-B4 provide feedback to the sender A on the expected protection level (indicated in the diagram as the integers 1, 3, 2, 5, where these integers are numbered in order of increasing protection level). The feedback is communicated back to A via intermediate nodes C1 and C2, who collect the respective feedbacks of devices in their respective groups G1 and G2 and process this, before returning a condensed acknowledge message representing both groups to sender A. The condensed feedbacks provided by these intermediate devices provides A with the same information on the minimum protection level that satisfies the expectations of all recipients as would have been the case if this information would have been forwarded to A without intermediate processing. (Here, we assume that the intermediate devices do not cheat in their calculations.)

Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto. 

1. A method of communicating between a sender and at least one recipient in a secure communication system, said method comprising the steps of: (a) said sender preparing a message having a header; (b) said sender determining a security level for said message based on known security requirements; (c) said sender including an indication of said security level in said header; and (d) said sender sending said message to said at least one recipient.
 2. (canceled)
 3. A method according to claim 1 wherein said header is divided into a plurality of frames, and each of said frames includes an indication of a security level, thereby allowing each of said frames to have a different security level to adapt to the nature of each of said frames.
 4. (canceled)
 5. A method according to claim 1 further comprising the steps of: (e) said at least one recipient receiving said message from said sender; (f) said at least one recipient extracting said indication of said security level from said header; and (g) said at least one recipient checking said security level to ensure it meets predetermined minimum requirements and rejecting said message if said security level is below said minimum requirements.
 6. A method according to claim 1 wherein said message is encrypted by said sender prior to sending said message.
 7. A method according to claim 1 wherein said message is signed by said sender prior to sending said message.
 8. A method according to claim 5 wherein said message is encrypted by said sender prior to sending said message and is decrypted by said at least one recipient subsequent to extracting said indication of said security level.
 9. A method according to claim S wherein said message is signed by said sender prior to sending said message and is authenticated by said at least one recipient subsequent to extracting said indication of said security level.
 10. A method according to claim 1 wherein said known security requirements include minimum security requirements for each of said at least one recipient and said sender.
 11. A method according to claim 10 wherein said security level is chosen to be high enough to meet all of said minimum security requirements.
 12. A method according to claim 1 wherein said indication of said security level comprises a number of security bits which change in length according to the application of said method.
 13. A method according to claim 1 wherein said sender receives a feedback response from said at least one recipient subsequent to sending said message, said feedback response including an update of said known security requirements.
 14. A method according to claim 5 wherein said at least one recipient sends a feedback response subsequent to checking said security level, said feedback response including an update of said known security requirements.
 15. A method of communicating between a sender and at least one recipient in a secure communication system, said method comprising the steps of: (a) said sender determining that an initial message is to be protected by a security level based on known security requirements, said determination made at a first layer of said sender; (b) said sender sending said initial message and an indication of said security level to a second layer of said sender; (c) said initial message undergoing cryptographic processing to generate a protected message at said second layer based on said indication of said security level using a shared key maintained between said sender and said at least one recipient; and (d) said sender sending said protected message to said at least one recipient.
 16. A method according to claim 15 further comprising the steps of: (e) said at least one recipient receiving said protected message at a first level, said first level similar to said second level of said sender; (f) said at least one recipient obtaining said initial message from said protected message using cryptographic processing based on said indication of said security level using said shared key; and (g) said at least one recipient passing said initial message and said indication of said security level to a second level, checking to ensure said security level meets predetermined minimum requirements, and rejecting said initial message if said security level is below said minimum requirements, said second level similar to said first level of said sender.
 17. A method according to claim 15 wherein said known security requirements include minimum security requirements for each of said at least one recipient and said sender.
 18. A method according to claim 17 wherein said security level is chosen to be high enough to meet all of said minimum security requirements.
 19. A method according to claim 15 wherein said indication of said security level comprises a number of security bits which change in length according to the application of said method.
 20. A method according to claim 15 wherein said sender receives a feedback response from said at least one recipient subsequent to sending said protected message, said feedback response including an update of said known security requirements.
 21. A method according to claim 16 wherein said at least one recipient sends a feedback response subsequent to checking said security level, said feedback response including an update of said known security requirements.
 22. A method of communicating between a sender and a group of at least one recipient in a secure communication system, said method comprising the steps of: (a) said sender determining a minimum security level at which to send a message, said minimum security level based on a value SEC_(A) indicative of security requirements of said sender and based on a value SEC_(G) indicative of security requirements of said group; (b) said sender sending said message with an indication of said security level to said at least one recipient of said group; (c) said at least one recipient receiving said message and said indication of said security level, determining if said message meets its own minimum security requirements, and sending a feedback response to said sender with an indication of said minimum security requirements; and (d) said sender receiving said feedback response and updating said value SEC_(G) based on said feedback response.
 23. A method according to claim 22 wherein said minimum security level is based on said value SEC_(A) only.
 24. A method according to claim 22 wherein said sender and said group are of the same entity, said method thus providing a self synchronization of said security requirements of said sender.
 25. A method according to claim 22 wherein said group comprises multiple groups and a central node intermediate of said sender and said multiple groups, said central node receiving multiple feedback responses from said multiple groups and communicating a single feedback response to said sender for updating said value SEC_(G).
 26. A method of communicating between a sender and at least one recipient in a secure communication system, said method comprising the steps of: (a) said at least one recipient receiving a message from said sender, said message having a header, said header including an indication of a security level determined by said sender based on known security requirements; (b) said at least one recipient extracting said indication of said security level from said header; and (c) said at least one recipient checking said security level to ensure it meets predetermined minimum requirements and rejecting said message if said security level is below said minimum requirements.
 27. A method of communicating between a sender and at least one recipient in a secure communication system, said method comprising the steps of: (a) said at least one recipient receiving a protected message from said sender at a first level, said protected message generated from an initial message, said initial message determined by said sender at a first layer of said sender to be protected by a determined security level based on known security requirements, said initial message sent with an indication of said security level to a second layer of said sender whereby said initial message undergoes cryptographic processing using a shared key maintained between said sender and said at least one recipient to generate said protected message, said first level of said at least one recipient similar to said second layer of said sender; (b) said at least one recipient obtaining said initial message from said protected message using cryptographic processing based on said indication of said security level using said shared key; and (c) said at least one recipient passing said initial message and said indication of said security level to a second level, checking to ensure said security level meets predetermined minimum requirements, and rejecting said message if said security level is below said minimum requirements, said second level of said at least one recipient similar to said first level of said sender.
 28. A method of communicating between a sender and a group of at least one recipient in a secure communication system, said method comprising the steps of: (a) said sender determining a minimum security level at which to send a message, said minimum security level based on a value SEC_(A) indicative of security requirements of said sender and based on a value SEC_(G) indicative of security requirements of said group; (b) said sender sending said message with an indication of said security level to said at least one recipient of said group to determine if said message meets minimum security requirements of said at least one recipient of said group; and (c) said sender receiving a feedback response with an indication of said minimum security requirements of said at least one recipient and updating said value SEC_(G) based on said feedback response.
 29. A method of communicating between a sender and a group of at least one recipient in a secure communication system, said method comprising the steps of: (a) said at least one recipient of said group receiving from said sender a message and an indication of a security level determined by said sender, said security level based on a value SEC_(A) indicative of security requirements of said sender and based on a value SEC_(G) indicative of security requirements of said group; (b) said at least one recipient determining if said message meets its own minimum security requirements; and (c) said at least one recipient sending a feedback response to said sender with an indication of said minimum security requirements for updating said value SEC_(G). 